1. Field of the Invention
This invention relates to insect control formulations. More specifically, this invention relates to the control by larvacidal activity of arthropods in the manure of livestock. Even more specifically, this invention relates to the control of arthropods through the formulation of insect growth regulators in a sustained-release bolus form which is orally administered to livestock.
2. Description of the Prior Art
Repeated application of insecticides directly to cattle is currently the most advanced method available to producers for the control of livestock pests. In fact, in the past 25 years, progress in control has been limited primarily to the development of new insecticides. However, the principal problem involved in the control of livestock pests is not unavailability of effective toxicants. Instead, it is the relatively short duration of effectiveness of the available compounds due to photodecomposition, evaporation, and adsorption of the materials, and to mechanical losses caused by rubbing of the animal and self-grooming.
Repeated treatment of livestock is expensive in terms of both labor and insecticide. To compensate for rapid degradation of the pesticides on animals, the producer must apply larger quantities than are necessary for control of the immediate population if toxic levels are to be maintained for any length of time. Such a practice is wasteful of insecticide, results in greater contamination to the environment, and increases the probability of toxicity to animals and of residues in animal products.
Therefore, one of the objectives of studies conducted at the U.S. Livestock Insects Laboratory, Kerrville, Tex., is to develop techniques that will make it possible to maintain the minimum effective level of toxicant on livestock over an extended period and thereby to increase the efficacy, efficiency, and safety of livestock pest control. This report deals with our efforts to use controlled-release technology against horn flies, Haematobia irritans (L.), common cattle grubs, Hypoderma lineatum (De Villers), and face fly, Musca autumnalis (DeGeer).
Boluses have been used in veterinary medicine to provide nutritional and therapeutic substances to animals for predetermined periods. But, for several reasons the technique has not been used in the control of livestock pests: (1) the effective dose of most conventional insecticides is usually too large for the bolus form to be practical; (2) many insecticides are degraded by the digestive processes of the animal and by the environment; and (3) conventional insecticides can accumulate in animal tissues and thereby produce objectionable residues. However, insect growth regulators (IGR's) are chemicals of another type and might be more acceptable in a bolus than conventional insecticides.
Insect growth regulators have been used successfully in the control of dung breeding pests of cattle for several years. Complete inhibition of development in manure has been achieved by administering insect growth regulators (IGR) to cattle in ground feed (Harris et al, 1973), in mineral blocks (Harris et al, 1974) and in drinking water (Beadles et al, 1975; Miller et al, 1976, 1977). Free-choice consumption and the resultant variations in dosage are inherent problems in the practical application of any of these techniques. Additionally, in some areas, animals will not consume supplemental minerals since their mineral requirements are amply met by the natural diet. The presence of untreatable sources of water (streams, rainfall) can interfere with the use of a water treatment.
The use of sustained-release bolus formulations is another approach to supplying animals with small daily dosages of materials. Boluses have been used in animal husbandry to provide nutritional and therapeutic substances such as trace elements, antibiotics, anthelmintics, animal hormones, and growth stimulants over predetermined periods of time. The prior art for these dosages forms is adequately described in patent literature such as, for example, U.S. Pat. No. 3,056,724 (Marston 1962), U.S. Pat. No. 3,507,952 (Rednick and Tucker 1970) and U.S. Pat. No. 3,535,419 (Siegrist and Katz 1970). However, bolus dosage forms have not been used in the control of livestock arthropods because the effective dosage of most conventional insecticides is usually too large to make the bolus form practical, many insecticides are destroyed by digestive process and environment, and conventional insecticides are often accumulated in animal tissues and, thereby produce undesirable residues.
The use of sustained-release bolus formulations to administer insect growth regulators for the control of livestock pests overcomes many of the aforementioned problems associated with ad lib treatments. Additionally, the efficacy and relative safety to insect growth regulators enables the use of the bolus treatment for long-lasting control measures.
An example of a veterinary composition is described in the literature, such as, for example, in U.S. Pat. No. 3,535,419. The patent discloses boluses which provide for the release of a progestational agent over an approx. 30 days for controlling and timing fertility.